The present invention is directed to improvements in magnetorheological (MR) fluid devices. More particularly, this invention is directed to semi-active MR fluid devices which are capable of damping motion along/about two or more longitudinal or lateral axes. The devices of this invention can damp motion of a damper or a mount having six degrees of freedom.
Commonly owned U.S. Pat. Nos. 5,277,281 and 5,284,330 describe and claim improvements to dampers involving improved dimensional relationships and sealless damper designs, respectively. The present invention incorporates some of the features of each of those patents and hence each is hereby incorporated by reference. The sealless designs of the present invention are preferably designed to have the dimensional characteristics of the '281 patent while the sealless designs of '330 have been modified to enable damping of multi-degrees of freedom.
MR devices are increasingly being proposed for a variety of uses including dampers, mounts, and tunable vibration absorbers. A number of technical hurdles are preventing implementation of these devices in several of the potentially attractive applications. First, MR fluid is highly abrasive and in dampers where seals are utilized to wipe fluid from a piston rod and retain the fluid within the damper's housing, the fluid quickly finds its way between the seal and piston rod surface and causes rapid deterioration of the seal's integrity.
Another problem which has been encountered is the settling of the iron particles out of the fluid. The MR fluid no longer has the characteristics it was designed to have in that portion of the fluid having reduced particle density nor in that portion having increased particle density.
In addition, most damper designs are configured to combat motion in a single axial direction. Lateral movement or torsional movement has not been a design consideration and, hence, the typical damper is unable to cope with such motion.
The MR device of the present invention overcomes each of these deficiencies of the prior art. Each of the embodiments of the present invention is capable of damping motion in up to six degrees of freedom (three translational and three torsional). Further, in keeping with the development of the '330 patent, by employing a sealless design, one of the key technical hurdles facing implementation of an MR fluid device is overcome. Finally, by utilizing a fluid with a consistency of a gel, the settling problem is overcome. Since the actual stroke length need for these sealless designs is so short, a thicker fluid is actually better. The MR fluid for use in these devices is preferably a water-based or water-glycol based fluid having a) iron loading of at least 45% by weight; b) an off-state viscosity greater than 1 Pa-s; and/or c) an off-state yield strength of at least 50 Pa. Because of the gel-like consistency of this MR fluid, a less expensive, coarser grade of iron can be used.
Various other features, advantages and characteristics of the present invention will become apparent after a reading of the following application.